Ocean Research

Eddies Could Provide Powerful Modes of Deep–Sea Transport
Researchers from Woods Hole Oceanographic Institution (WHOI) and their colleagues have found that massive ocean eddies can reach all the way to the ocean bottom at mid–ocean ridges, some 2,500 meters deep, transporting tiny sea creatures, chemicals and heat from hydrothermal vents over long distances.

The discovery, reported in the April 28 issue of Science, helps explain how some larvae travel huge distances from one vent area to another, said Diane K. Adams, lead author at WHOI and now at the National Institutes of Health. The potential for ocean transport, however, is what that Adams and her colleagues found particularly intriguing.

Because the eddies appear to form repeatedly, the high–speed, long–distance transport can last for months.

"Although the deep–sea and hydrothermal vents in particular are often naively thought of as being isolated from the surface ocean and atmosphere, the interaction of the surface–generated eddies with the deep sea offers a conduit for seasonality and longer–period atmospheric phenomena to influence the 'seasonless' deep sea," Adams and her colleagues wrote.

The eddies appear to form seasonally, suggesting repeated interactions with undersea ridges such as the Eastern Pacific Rise. The models "predict a train of eddies across the ocean," Adams said. "There may be two to three eddies per year at this location."

Melting Ice on Arctic Islands a Major Player in Sea Level Rise
Melting glaciers and ice caps on Canadian Arctic islands play a much greater role in sea level rise than scientists previously thought, according to a study led by a University of Michigan (UM) researcher.

The 550,000–square–mile Canadian Arctic Archipelago contains some 30,000 islands. Between 2004 and 2009, the region lost the equivalent of three–quarters of the water in Lake Erie, according to the study. Warmer–than–usual temperatures in those years caused a rapid increase in the melting of glacier ice and snow, said Alex Gardner, a research fellow in UM's Department of Atmospheric, Oceanic and Space Sciences who led the project. The study was published online in Nature in April.

"This is a region that we previously didn't think was contributing much to sea level rise," Gardner said. "Now we realize that outside of Antarctica and Greenland, it was the largest contributor for the years 2007 through 2009."

Ninety–nine percent of all the world's land ice is trapped in the massive ice sheets of Antarctica and Greenland. Despite their size, they only account for about half of the land–ice being lost to oceans, partly because they are cold enough that ice only melts at their edges. The other half of the ice melt comes from glaciers and ice caps in the Canadian Arctic, Alaska and Patagonia. The study shows the importance of these smaller, often overlooked regions, Gardner said.
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Sea Level Rise May Return to the West Coast After 30–Year Hiatus
The West Coast of North America has caught a break that has left sea level in the eastern North Pacific Ocean steady during the last few decades, but researchers said there is evidence a change in wind patterns may be occurring that could cause coastal sea level rise to accelerate beginning this decade.

In May, researchers at the Scripps Institution of Oceanography at the University of California, San Diego, said conditions dominated by cold surface waters along the West Coast could soon flip to an opposite state. This would cause coastal ocean waters to become characterized more by a downwelling regime, where the amount of colder, denser water currently brought to the surface will be reduced. Resulting warmer surface water will raise sea level.

Global sea level rose during the 20th century at a rate of about two millimeters per year. That rate increased by 50 percent during the 1990s to a global rate of three millimeters per year, an uptick linked to global warming.

Researchers studied wind stress patterns that characterize the different phases of Pacific Decadal Oscillation (PDO). Wind stresses can act to alter the characteristics of the coastal upwelling and downwelling regime. The authors wrote that wind stress variability over the eastern North Pacific "recently reached levels not observed since before the mid–1970s regime shift. This change in wind stress patterns may be foreshadowing a PDO regime shift, causing an associated persistent change ... that will result in a concomitant resumption of sea level rise along the U.S. West Coast to global or even higher rates."

Agulhas 'Leakage' May Stabilize Atlantic Overturning Circulation
The Agulhas Current, which runs along the east coast of Africa, may not be as well known as its counterpart in the Atlantic, the Gulf Stream, but researchers are taking a closer look at the current and its "leakage" from the Indian Ocean into the Atlantic Ocean.

The Agulhas Current transports warm, salty waters from the Indian Ocean to Africa's southern tip, where most of the water loops around to stay in the Indian Ocean, and some waters leak into the fresher Atlantic Ocean via giant Agulhas rings.

Once in the Atlantic, the Agulhas leakage waters eventually flow into the Northern Hemisphere and act to strengthen the Atlantic overturning circulation by enhancing deepwater formation.

Agulhas leakage could be a significant player in global climate variability, according to a team of scientists led by University of Miami associate professor Lisa Beal, who published a study in Nature in April about the current.

Recent research points to an increase in Agulhas leakage over the last few decades caused primarily by human–induced climate change. This finding is profound, the scientists said, because it suggests increased leakage could strengthen the Atlantic overturning circulation. Warming and accelerated meltwater input in the North Atlantic has been predicted by many to weaken the overturning circulation.
For more information, visit www.sciencedaily.com.

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